It was the first and worst year of the S80 and even though Volvo has tryed to fix some of the more minor, irratating problems with them through campaigns, it's still one of the worst Volvos ever made in recent times IMO.
There's a buttload of them all over now as they've come off their leases so they can be found at many dealers cheaply and even "certified" BUT they're still a major "buyer beware" as being leased cars, most of their former owners did NO maintenance to them thus I highly doubt they'll be decent 2nd hand cars for most people.
The '99 S80 trans was known to have issues so it's just a matter of time and it'll fail. Oil pan, oil sump related o-rings are deteriorating so eventually the engines start ticking and if not caught in time, more serious engine damage could occur due to low oil pressure. The early S80s were/are plagued with all sorts of premature front suspension problems, it's been one thing after another. Throttle units and MAF meters are also common failure items.

If you want an S80, get a '02 or newer as by then they've pretty much worked the bugs out of them.